Coat a large skillet with nonstick cooking spray. Cook chicken in the skillet over medium-high heat until no longer pink and cooked through.
In a 3-1/2- or 4-quart slow cooker stir together the pizza sauce and chopped vegetables. Stir in cooked chicken or turkey.
Cover and cook on low-heat setting for 6 to 8 hours or on high-heat setting for 3 to 4 hours.
Arrange split buns, cut sides up, on an unheated broiler pan. Broil 3 inches from the heat for 1 to 2 minutes or until toasted. Spoon meat mixture onto toasted roll bottoms. Top each with a slice of cheese and top halves of buns. Makes 8 sandwiches.